1. Field of the Invention
The present invention relates generally to the field of stroke and angiogenesis. More specifically, the present invention relates to stroke-generated angiogenesis enhancers and uses thereof.
2. Description of the Related Art
Brain recovery from stroke is a complex system involving the restoration of blood supply (angiogenesis) and neurons (neurogenesis) to the affected area. For angiogenesis, endothelial cell proliferation can occur as early as 12 to 24 hours. These newly generated cells then migrate towards ischemic brain regions in response to a number of endothelial cell mitogens such as vascular endothelial cell growth factor (VEGF) and platelet derived growth factor (PDGF) and form new blood vessels in peri-infarct cortex after 3-7 days. Angiogenesis then continues for at least 21 days. Importantly, niaspan, a drug that increases post-stroke angiogenesis in rodents, improves functional stroke recovery, suggesting that enhancing post-stroke brain angiogenesis could result in improved stroke outcomes. Furthermore, brain angiogenesis is different from non-brain angiogenesis due to unique properties of the brain vasculature including formation of the blood-brain barrier, embedment in a neuronal-glial milieu, different matrix receptor expression, and relative refractoriness to angiogenesis after development.
Ohab et al. (1) have demonstrated in rodents that after stroke migrating immature neurons (neuroblasts) associate with remodeling blood vessels in a “neurovascular niche” that causally links reparative angiogenesis and neurogenesis. The newly produced vasculature promotes neurogenesis by production of various growth factors and appears to serve as a scaffold for newly born neurons that allows them to migrate towards infarcted tissue. In addition to maturing neurons and endothelial cells, the neurovascular niche contains extracellular matrix (ECM) that is secreted and actively remodeled during angiogenesis to allow cellular migration and blood vessel morphogenesis. One such extracellular matrix component, perlecan, is essential to the neurovascular niche. Its absence in mice results in severely impaired neurogenesis due to the loss of neurogenic factor capturing that perlecan provides to support neurogenesis.
Matrix remodeling during and after stroke is an important part of brain repair after injury and repair that further points to the importance of perlecan. In stroke, dying and infiltrating inflammatory cells release matrix metalloproteinases (MMPs) which disturb the blood brain barrier and proteolytically process the extracellular matrix. Although the initial processing and degradation of extracellular matrix is largely thought of as a negative consequence of stroke, one consequence of matrix proteolysis is the generation of bioactive matrix fragments. Indeed, many matrix components are known to harbor bioactive matrix fragments in their C-terminal regions that can inhibit angiogenesis outside of the central nervous system (2-3). Perlecan has the distinction of being the most sensitive and rapidly processed matrix component after stroke. Perlecan proteolysis occurs within 2 hours of the occlusion of the middle cerebral artery in nonhuman primates and persists for at least 7 days.
Perlecan is composed of five domains, each with sequence homology to other proteins. The C-terminal fragment of perlecan known as domain V (DV or endorepellin) consists of three laminin globular (LG) domains, each separated by two epidermal growth factor (EG)-like domains. Domain V and its LG3 fragment are normally found in the human urinary, blood and cerebrospinal fluid proteomes. Domain V, by binding to the α2 subunit of the α2β1 integrin, inhibits several angiogenic functions of nonbrain endothelial cells including migration and capillary morphogenesis. Domain V interaction with α2β1 appears to be different than that of pro-angiogenic collagen with α2β1 resulting in opposing outcomes. Domain V has been characterized as anti-angiogenic in several endothelial cell types of nonbrain origin (4-5).
Despite this, the prior art is deficient in angiogenesis enhancers. The current invention fulfils this long standing need in the art.